virt: vmgenid: drop owner assignment

ACPI bus core already sets the .owner, so driver does not need to.

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>